Fix wrong model recognition

Parser was recognizing words with `model` keyword combination, for example `` `model` `` or `Cmodel`, as model, this is a suggestion to fix the issue. this pull request would close issue #92 and #152.
I guess this is the way to go for now

```
^[[:blank:]]*([^][()]+[[:blank:]]+)?[Mm]odel" MEDIA_TYPE "?[[:blank:]]*"
```
Major drawback is there is no SYMBOL_IDENTIFIER macro in it (making it hard when you need to change the SYMBOL_IDENTIFIER) policy. The minor drawback is we are not using the symbol identifier macro the identifier needs to be trimmed but that should be done anyway. 

Or using `SYMBOL_IDENTIFIER` (beware this introduce one extra capture group!):

```
^[[:blank:]]*" SYMBOL_IDENTIFIER " ?([[:blank:]]+))?[Mm]odel([[:blank:]]*\(([^\)]*)\))?[[:blank:]]*$
```